Step 11.1: Piggyback Sliders as XY Table

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Step 11.1: Piggyback Sliders as XY Table

About Piggyback Sliders

The Piggyback Slider configuration is two Sliders:

Slider(A) : moves along the X-axis of the Mechanism-Plane

Slider(B) :  mounted to Slider(A), and moves along the Y-axis of Slider(A)

The Piggyback Slider Configuration is only one way to model an XY-Path.  

You can also use a Motion-Path. See: Motion-Path and Blend-Curves.


The Sliders do not need to be in the X-axis and Y-axis directions or even it right-angles to each other. We describe them in these directions for convenience only.

For example, they may be in the Radial and Tangential direction relative to a radius of a circle.


Mechanical Systems that follow the XY Motion-Path:

Linear-Slides (Slide-ways + Slide-blocks)

The Piggyback Sliders are built in the same way as X-Y Tables that use Linear-Motion Technology (the motors and the mechanics).

The motors that drive the Sliders have the same nominal* motion as the Piggyback Sliders. See Step 11.1

* For example, a motor may rotate a Pulley to move a Belt, or a Ball-Screw to move a Nut. In each case, the motors rotate a different number of rotations, but their rotation is a linear relationship to the Slider's motion.

Linear Slides with Dyads

a.Start with Piggyback Sliders for the X-Y-Table.

b.Connect Dyads between the sliders and the machine-frame.

c.Use cams or servomotors on the Machine Frame to drive the Dyads and thus the XY-table

Add motions to the Piggyback Sliders / XY-table directly. MechDesigner will use inverse-kinematics to calculate the motions for the cam-followers or servomotors - See Step 11.2

Translating Beam (a Part that moves on the Mechanism-Plane but does not rotate)

It is possible to model a translating-beam that does not physically use linear-slides.

Look at this video. This example happens to show 3 independent axes to control the motion of a Beam. In this case the motion of the beam can be specified to translate or rotate.

Use Piggyback Sliders to specify the X-Y Motion-Path, even though they are not in the mechanical system. See Step 11.3.

Technical Note:

Rectilinear Translation: All points in a Part have the same translating and parallel motions.

Curvilinear Translation: All points in a Part have the same, but not necessarily straight, motions.

Quick Instructions: Add Piggyback Sliders

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Quick Instructions:

STEP 1.Add the X-SliderRed-14-1b to a horizontal Line in the Base-Part

STEP 2.Edit the X-Slider. Add a Line that is parallel to the Y-axis

STEP 3.Add the Y-SliderRed-14-2 to the Line that is parallel to the Y-axis of X-Slider.

STEP 4.Design the motions for each Slider.

STEP 5.Add a Trace-PointRed-14-4 to a PointRed-14-3 that moves with the Y-Slider.

STEP 6.Run menu  > Cycle to watch the Piggyback Sliders.

More Detailed Instructions: Add Piggyback Sliders

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Add the X-Slider

STEP 1.Edit the Base-Part

STEP 2.Part-Editor: Geometry toolbar > Add Line , Constraints toolbar > Add Horizontal : Click the Line; Close the Part-Editor

STEP 3.Mechanism-Editor: Add a Part; Add a Slide-Joint between the Part and the Line in the Base-Part

STEP 4.Mechanism-Editor: Add a Motion-Dimension FB to identify the X Slider

STEP 5.Mechanism-Editor: Add a Linear-Motion FB and a Motion FB to the graphic-area Connect the FBs with wires.

STEP 6.Rename the Slider to X SLIDER

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Edit the X-Slider, Add a Vertical Line

STEP 1.Mechanism-Editor: Edit X-Slider Part : Part-Editor:  Edit length to 100mm.

STEP 2.Part-Editor: Geometry toolbar > Add Line , Drag UPWARDS to add the Line : Constraints toolbar > Add Vertical click the Line;

STEP 3.Part-Editor: Geometry toolbar > Add Dimension :Line = 100mm

STEP 4.Part-Editor: Constraints toolbar > Coincident , Click start-Point of the two Lines .

STEP 5.Close the Part-Editor

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Add the 'Y'-Slider

STEP 1.Mechanism-Editor: Add a Part; Add a Slide-Joint between the new Part and the vertical Line in the X-Slider

STEP 2.Mechanism-Editor: Add a Motion-Dimension FB to specify the Position of the Y-Slider.

STEP 3.Mechanism-Editor: Add a Linear-Motion FB and a Motion FB to the graphic-area

STEP 4.Mechanism-Editor: Connect the FBs

STEP 5.Rename the new Slider to Y-SLIDER

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Get Motions for the Sliders

STEP 1.Mechanism-Editor: Double-click the Motion FB connected to the X-Slider to open the Motion FB dialog-box

STEP 2.Mechanism-Editor: Click the X-Motion in the drop-down box for the X-Slider, Close the Motion FB dialog-box

STEP 3.Mechanism-Editor: Double-click the Motion FB connected to the Y-Slider to open the Motion FB dialog-box

STEP 4.Mechanism-Editor: Click the Y-Motion in the drop-down box for the Y-Slider Close the Motion FB dialog-box

Show the Path traced out by the Y-Slider

STEP 5.Mechanism-Editor: Do Kinematic-element > Add Trace-Point , click a Point on the Y-Slider

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STEP 7: Run menu > Cycle (or ALT+C)


X Motion

This is a motion for the X-axis.

Use a Motion FB to link this motion to the Motion-Dimension FB to move the X-Slider.

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Y Motion

This is a motion for the Y-axis.

Use a different Motion FB to link to the Motion-Dimension FB to move the Y-Slider.


These two example motions define the motion along the XY-path on the Mechanism-Plane

We show the  XY-path in the graphic-area with a Trace-Point.

Degrees-of-Freedom of Piggyback Sliders

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Degrees-of-Freedom and Mobility of Piggyback Sliders

Gruebler Equation to find the number of Degrees-of-Freedom (F):

F = 3(P-1) – 2J  : P = Number of Parts (1 × Base-Part + 2 × Added-Parts) ; J = Number of Joints ( 2 × Slide-Joints)

F = 3×(3-1) – 2×2

F = 6 – 4 = 2

Mobility = # Degrees-of-Freedom(F) – # Motion-Dimensions = 2 – 2 = 0.

Kinematics Tree of Piggyback Sliders

KT-PiggybackSliders

Kinematics-Tree for Piggyback Sliders.

There is:

One kinematic-chain (Solved Mechanisms)

The Solved Mechanism has:

Two Sliders

Machines that use Piggyback Sliders

Example machines include:

Pen Plotters

Water-Jet Cutters

Laser Markers or Cutters

 

An XY-Gantry Robot

Look at the video to the left.

This 'Plotter' moves a Pen along a slide, say the Y-axis slide. The X-axis carries the Y-axis slide.  The combined movement plots the drawing.

With this machine, there is an EXACT linear-equivalence between the XY-Path and the control positions of the slider motors. The system is Kinematically Linear.

This 'Plotter' moves a Pen with a slider along the X-axis. A different slider carries the X-axis slider, but along the Y-axis. The two movements of the slider plot the drawing.